The German FluxCrawl robot has been tested during renovation work on a bridge in Mettlach

FluxCrawler robot checks safety of elevator cables

A 70cm-long robot detects cracks and fissures in bearer cables of elevators or cable cars before they can cause harm.

The FluxCrawl robot, developed and patented by scientists at the Fraunhofer Institute for Nondestructive Testing IZFP, is designed to scan surfaces of heavily loaded metal cables by performing a magnetic flux test.

The metallic caterpillar-like robot climbs up the cable, revolving around, attached to the cable by a U-shaped magnet. It creates a magnetic field in the analysed wire, which is then measured by sensors in the core section of the device.

Whenever the cable is damaged, the magnetic field shows signs of disruption. The sensors pick up the anomaly quickly and accurately and are even capable of spotting the exact angle and position of the tiniest crack – something that hasn’t been possible to achieve with conventional methods relying on conductive coils.

“If such micro-fissures are not discovered in time, the steel can break. This is why material checks are absolutely vital to avoid deadly consequences or even catastrophes”, said Dr Jochen Kurz, an engineer and department head at IZFP in Saarbrücken.

The main shortcoming of the previously used coils, the researchers said, is in their inability to accommodate cables of all sizes and diameters. On the contrary, the robot is comfortable with all cables between four and 20 centimetres.

Its moving up the cable is controlled via Bluetooth. The image of the magnetic field induced in the cable is transmitted to the controlling computer, where it can be analysed in greater detail.

To enable the robot to examine properly areas difficult to access – such as where cables are anchored - an extra-method has to be employed. Using a transducer, the engineers can create an ultrasound wave that penetrates the material. Whenever the wave hits a flaw in the cable, signal is sent back to the computer model. That way, interior of the cable can be analysed with unprecedented precision.

A test project has been recently running on a bridge in Mettlach, Germany, that is undergoing reconstruction. However, load bearing cables are of a concern to every elevator, crane, cable car or ski-lift operator. The researchers therefore believe the technology has a promising future in many sectors.

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